The commander of the British-German-Netherland army at Waterloo in 1815 was the talented Field Marshal Arthur Wellesley, 1st Duke of Wellington. (He became field marshal in 1813.) He campaigned in India, Netherlands, Denmark, Portugal, Spain and France. Wellington raised the reputation of the British
to a level unknown since Marlborough.

In April 1815, Wellington reorganized the Allied Forces in Netherlands. The British and Hannoverian troops were merged with the Dutch-Belgian troops. In April-June Wellington's army was reinforced with Brunswick and Nassau troops.
At Waterloo the allied army consisted of 53,850 infantry, 13,350 cavalry, 5,000 artillery and 1,000
sappers, miners etc.

Wellington was worried about possible French attack up the Mons-Hal-Brussels route despite
no reports of such a movement. He posted at Hal 17,000 troops to check such an advance.
Had Wellington lost at Waterloo he would have great difficulty justyfying so many men idle 2-3 hours
march away.

The size of allied troops varied.
Some historians emphasize the fact that at Waterloo the British battalions were understrength.
This is correct. But this is not the whole picture. Although understrength,
the average British battalion was stronger by 145 muskets than average French battalion.
The largest battalion on the battlefield was the British I/52nd Foot, 1130 men (!)
The battalions of British Foot Guard averaged approx. 1000 men.
The smallest battalion on the battlefield was the French III/108th Line Regiment. It consisted of 251 men.
Average infantry battalion : - 665 men / British - 610 men / Prussian - 520 men / KGL - 520 men / French
Average squadron : - 145 men / Wellington's cavalry - 135 men / Napoleon's cavalry - 115 men / Blucher's cavalry

* - MG Sir George Murray
He was Quartermaster General during the Peninsular War (1808–11 and 1813-14).
He was briefly in Canada (Dec 1814 - May 1815) where he was appointed provisional Governor
of Upper Canada and reviewed the defences along the border with the hostile USA.
The Americans declared war in 1812 for a number of reasons, including trade restrictions, impressment of American merchant sailors into the Royal Navy, British support of American Indian tribes against American expansion, and the humiliation of American honor. Until 1814, the British Empire adopted a defensive strategy, repelling multiple American invasions of the provinces of Upper and Lower Canada.

** - Prince of Orange .
Willem Frederik George Lodewijk was born in 1792. He was the eldest son
of King William I of the Netherlands and Wilhelmine of Prussia. Willem Frederik entered
the British Army, and in 1811, as ADC to Wellington, took part in campaigns
of the Peninsular War.
He returned to the Netherlands in 1813 when his father
became king. In 1815, Willem Frederik became crown prince and he took service in the army
when Napoleon escaped from Elba.

Notes:
* - left in Brussels, not present at Waterloo
** - not present at Waterloo
*** - this battery was at Vilvordse, not present at Waterloo
**** - this battery was at Ostend, not present at Waterloo

Bourbon Cavalry Corps
- Duc de Berry (picture below)
This unit consisted of French deserters willing to fight for King Louis XVIII's cause.
They were horse carabiniers, cuirassiers, dragoons and even some grenadiers and
chasseurs of the Old Guard. Squadrons were commanded by generals (royalists).
They took no part in the battle.

Russian Order of Battle - Waterloo Campaign 1815.
The plan devised by General Gneisenau was founded on the enormous numerical superiority of the Allies in 1815. Gneisenau said:
"For great armies, the fourth of which (the Russian Army) will form the Reserve, will enter France simultaneously and march
straight on to Paris. Whatever happens to one of the three armies (Prussian, British-Netherland, and Austrian) of the
first line,
whether it be beaten or not, the two others will continue to advance leaving detachments in their rear to watch the fortresses.
The mission of the Russian Army is to retrieve any misfortune which may overtake either of the armies of the first line."
The Russians crossed Poland, Prussia, and several German states rapidly.
Chernishev's cavalry and Cossacks crossed the Moselle River and carried by storm, on 3 July, the city of Châlons-sur-Marne.
The French garrison had promised to make no resistance, and yet fired upon the Russian cavalry; whereupon the Russians immediately dismounted, scaled the ramparts, broke open the gates, and sabred a part of the garrison. They also made the remainder prisoners, including the French General Rigault, and pillaged the town. The bulk of the Russian army reached
Paris in mid July. The news of the capture of Paris by the Prussian and British troops led to a suspension of hostilities; which
was concluded on 24 July 1815.